Kiln structure



. tunnel of the kiln.

Patented Oct. 10, 1950 UNITED STATES PATENT OFFICE KILN STRUCTURE Application June 13, 1946, Serial No. 676,500

3 Claims. 1

This invention relates to kilns, and more particularly to certain improvements in direct fired kilns of the type used in burning ceramic ware.

Tunnel kilns for burning ceramic ware such as pottery, tile, bricks, etc., have long been used in the ceramic industry. These kilns may be either of the straight-through or circular type or of other curved form and also may be either directly or indirectly fired. In indirect kilns the products of combustion from the burners which supply heat to the ware are kept out of contact with the ware by a suitable mufiie arrangement. In direct fired kilns the products of combustion circulate around and contact the ware as it moves through the preheating and burning sections of The present invention is particularly adapted to direct fired kilns.

The ware to be burned is moved through a tunnel kiln on cars and: the usual kiln arrangement includes a preheating section, a burning or firing section, and a cooling section. In the preheating section the ware is raised to a point rather close to the burning temperature. The hottest part of the kiln is in the burning section where the actual burning or firing of the ware takes place. Relatively slow and controlled cooling is accomplished as theware passes out through the cooling section. It is customary to provide means for heating ware on the cars as they pass through the preheating section by applying waste heat from the burning section, heat given off by the Ware in the cooling section and, in some cases, primary heat from fuel supplied at the preheating section.

In the usual direct fired tunnel kiln the tunnel is of substantially uniform cross section throughout the preheating section and is abruptly widened out at the burning section to provide a combustion or heating chamber of adequate volume in the burning section. The ware is loaded on the cars so that the width of the load is almost equal to the narrowest width of the tunnel, leaving only enough clearance on each side of theload to prevent striking the tunnel walls and permit adequate flow of gases; The line which defines the path of the side of a kiln car load of maximum width may be referred to as a "tunnel line. In prior kilns a substantial and relatively sharp temperature'increaseoccurred between the end of the preheating section and the beginning of the burning section. This tem perature differential caused a relatively sudden increase in the temperature of the ware as it entered the burning section with possible blistering,. cracking, warping; andother undesirable results from shock heating. Ware has custom-- arily been loaded on the cars of this type of kiln with one or morelongitudinal passages extending throughthe load, thus forming a flue or iiues through the ware to permit more adequate and uniform heating thereof. However even this provision does not overcome the shock heating difficulties encountered as the ware passes from the preheating into the burning section of a direct fired kiln. It i therefore among the objects of my present invention to provide a kiln structure having a preheating zone and a burning zone together with means for preventing an excessively sudden temperature rise in ware moving from the preheating into the burning section.

Other objects of my invention include: the provision of a tunnel kiln of the type described in which cracking, warping, blistering, and other damage to the ware as it moves from the preheating to the burning zone is prevented; the provision of a heating apparatus which will evenlyand smoothlyra-ise the temperature of articles passed through the apparatus; the provision of a direct fired: tunnel kiln in which the gas velocity aroundand past the loads on the cars isreduced from that encountered in previous tunnel kilns; the provision of a ceramic kiln structure which can be operated at a relatively high production rate and in which breakage, Warping, and other defects are reduced to a minimum; and the provision of a tunnel kiln structure which is economical to construct and maintainand which gives a higher production output with less breakage than previously proposed tunnel kilns. V

The above and other objects of my invention will appear from the following description of several embodiments thereof, reference being had to the accompanyingv drawings, in which:

Figure 1 is a diagrammatic, fragmentary, horizontal. plan section showing the burning section and. a. portion of the preheating section of a direct fired tunnel kiln embodying my invention.

Figure 2 is a view generally similar to Figure 1 but showing a modified form of my improved kiln structure.

Figure 3 is a view similar to Figures 1 and 2 but illustrating a third form of my kiln structure.

Figure 4 is a fragmentary vertical cross sectional view taken substantially on line 3-8 of Figure 2.

Figure 5 is a transverse vertical cross sectional view takenonline 5-5 of the kiln shown in Figure 2, a loadedkiln car being shown in the tunnel.

In Figure 1, the kiln illustrated is of the straight-through, direct fired, tunnel type and includes a high temperature or burning section indicated at B, a preheating section, a portion of which is indicated at P, a transition zone which may be considered as a part of the preheating section and which is disposed at the junction of the preheating and burning sections and is indicated at T, and a cooling section which extends beyond the burning section B and is indicated at C. The sections P, B and C are arranged in adjoining end to end relation and form a tunnel like ware passage. Tracks Ill extend through the kiln tunnel in the usual manner and it will be understood that, when in operation, a continuous line of loaded kiln cars will be moving through the tunnel on the tracks ID in the direction of the arrow. The maximum load width is indicated by the tunnel lines L and the width of the tunnel in the narrow or standard part of the preheating section is indicated at P. In the burning section the tunnel chamber is widened out as indicated at B to provide combustion or heating chambers along side the tunnel lines L. The cooling section C has a width C which is usually and preferably substantially the same as the width P' of the preheating section.

As is seen in Figure the load H on the kiln car l2 has relatively small clearance from the side walls l3 and M of the preheating section P. In previously constructed kilns with which I am familiar the preheating section extends up to the burning section and the relatively narrow tunnel width P is maintained all the way to the entering end of the burning section B. Thus, in the prior kilns, the sides of the loads on the cars are closely adjacent the tunnel walls until the cars enter the burning section. Also, in the prior kiln structures, there was a substantial temperature differential between the exit end of the preheating section and the enterin end of the burning section. For example, the temperature in the burning section might be 1950 F. while the temperature in the preheating section immediately adjacent thereto might be 1750 F. This is especially true on rapid firing cycles through the kiln. The undesirable shock heating effects referred to above resulted because of the sudden and substantial rise in temperature which took place as the ware moved from the preheating into the burning section.

To overcome this objectionable condition, I provide what I have termed a transition zone or section T which is situated at the entering end of the burning section. This transition zone is properly considered as part of the preheating section P as its function is to assist in proper preheating of the ware. It consists of a portion of the kiln tunnel having a width T which is greater than the width P of the forward or entering portion of the preheating section but less than the width B of the burning section. Thus, as seen in Figure l, stepped back offsets or enlargements I5 and [6 are provided extending a substantial distance from the end of the burning section toward the entrance end of the kiln. Although I have referred to the portion T of the kiln as a transition zone it may, as noted above, be considered as a part of sub-section 0f the preheating section and I have found that, in some cases, the offset or set back tunnel walls described herein may advantageously extend from the entering end of the burning section back to the entrance to the kiln tunnel.

Burner ports I! of the usual type are provided in the burning section B and suitable burners, not shown, will be located to discharge into the burning section through these ports. Auxiliary burner ports l8 are preferabl provided in the transition zone T and suitable burners, not shown, will also be provided to supply heat through these ports. It will be understood that in some instances it may be unnecessary to supply auxiliary heat through the ports I8, and that any number of burners may be used to give the proper heating effect which will result in a smooth heating curve, free from sudden increases of temperature, as the ware moves through the preheating zone into the burnin zone. The normal draft through a kiln of this type is in a direction opposite to the movement of the cars through the kiln and may be created by a suitable stack or suction fan disposed at the inlet end of the kiln and connected to the tunnel by suitable ports and passages in well-known manner. Thus hot gases will flow from the burning section B into and through the transition zone T to the exhaust ports of the preheating section where they are withdrawn.

In Figure 2 a modified form of my kiln structure is illustrated in which the transition zone T extends farther toward the entering end of the kiln than in Figure 1 and includes a. pair of offset portions l9 and 20 and a wider pair of offsets 2| and 22. The width of the tunnel at the offsets l9 and 20 is indicated at T while the width of the tunnel at the offsets 2| and 22 is indicated at T. This arrangement results in a generally tapered transition zone portion of the preheating part of the kiln, the zone having its greatest width I adjacent the burnin section B and being narrowest at its entering end.

A third form of kiln embodying my invention is shown in Figure 3 in which the transition zone T has angularly disposed diverging side walls 23 and 24 which form a smoothly enlarging transition zone extending from a point in the preheat section to the burning section. In some cases the side walls of the tunnel may be made to start to diverge as far away from the burning section as the entrance or charging end of the kiln. Gases are withdrawn from the kiln at the exhaust portion (not shown) which may be located closely adjacent the entering end of the kiln tunnel in well known manner.

It will be understood that, although I have referred to the transition zone as being a somewhat independent part of the preheating section of the kiln, these portions of the kiln structure are not sharply defined either structurally or functionally. The primary purpose of the entire kiln structure which lies in advance of the burning section is to bring the ware on the cars quickly and smoothly up to burning temperature so that sudden and excessive temperature changes will not occur when the cars enter the burning section. Thus the portion of the tunnel from the ware entrance to the burning or high temperature section is actually a preheating section.

With my improved kiln structure the temperature in the tunnel immediately ahead of the burning section may, for example, be about 1900 F. when the temperature in the entering end of the burning section itself is about 1950 F. As mentioned previously, the temperature differential at this point in prior kilns was usually much greater. This resulted at times in damage to the ware due to shock heating and to overcome this condition required slowing down the travel of the cars through the kiln with a resulting decrease in output and efficiency. Burner ports 25 are provided in the burning section of the structures shown in Figures 2 and 3 and burner ports 26 are adapted to supply heat directly to the transition zone in the same manner as burner ports l8 of Figure 1.

As was mentioned above it has been customary to leave longitudinal passages or flues through the Ware as it is loaded on the kiln cars and such passages are seen at 21 and 28 in Figure 5. These passages are preferably provided in loads charged into my improved kiln structure and permit hot gases to pass longitudinally through the central portion of the load on the cars. My improved offset or tapering transition zone arrangement permits hot gases to contact the outer sides of the load, as well as the interior through the flue or fiues 21 and 28, in a controlled manner which eliminates the sudden rise in temperature which previously occurred between the exit end of the preheating zone and the entering end of the burning zone.

I have described herein several types of kiln structure which embody the principles of my improved means for preheating ceramic ware prior to its entrance into the burning section of a kiln. Although I have described in considerable detail the illustrated embodiments of my invention, it will be understood that numerous variations and modifications may be made in the kiln structure without departing from the spirit of my invention. The drawings accompanying this specification are rather diagrammatic for purposes of simplicity and those skilled in the art will appreciate that various standard and usual kiln features in the nature of blowers, exhaust fans, ventilating ports, hues and other openings in the tunnel walls may be provided. Furthermore, the length of the portion of the kiln structure which I have referred to as a transition zone may be varied from a relatively short enlargement of the tunnel immediately ahead of the burning section to a, long tapering tunnel section gradually reducing in width from a maximum at the burning section entrance to a minimum, which is preferably the same as th normal tunnel width, at or adjacent to the kiln door or entrance. I do not, therefore, wish to be limited to the exact kiln structures herein shown and described but claim as my invention all embodiments thereof coming within the scope of the appended claims. 1

I claim:

1. In a direct fired kiln apparatus of the type described, a tunnel structure having a ware entrance and side walls and including a preheating section and a high temperature section in adjoining end to end relation, fuel burner means for directing products of combustion into direct contact with ware in said high temperature section of said tunnel structure, said side walls in said preheating section being spaced closer together at said entrance than at the junction of said preheating and high temperature sections and. forming a preheating section the width of which increases from a point spaced from said high temperature section to the junction of said preheating'and high temperature sections.

2. An apparatus as described in claim 1 characterized by a cooling section in adjoining end to end relation with the high temperature section, said cooling section being narrower in transverse cross-sectional dimension than said high temperature section.

3. An apparatus as described in claim 1 characterized by independent means for supplying heat to the preheating section.

JAMES T. ROBSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,223,732 Reams Apr. 24, 1917 1,590,462 Wilson et al June 29, 1926 1,646,254 Meehan Oct. 18, 1927 1,652,570 Hanley, Jr. Dec. 13, 1927 1,662,912 Wilson et'al. Mar. 20, 1928 2,003,451 Ladd June 4, 1935 2,010,261 Hartford Aug. 6, 1935 2,159,965 Dressler 1;.-- May 30, 1939 

